Plastic waste such as PET beverage bottles, blister packages made of PET (thermoformed PET films), plastic waste consisting of polyolefins or the like, must be cleaned during recycling. Very high quality requirements must be satisfied. The permissible impurities fluctuate within the ppm range. For cleaning, the plastic waste is first comminuted into shredded plastic, in particular so-called plastic flakes. Shredded plastic that has been optimally comminuted beforehand is a requirement for the cleaning process and continuous feeding of a cleaning system. In particular, the shredded plastic should be generated as evenly as possible with a small amount of fines. It is known to use a shredder for this (a rotor with blades and opposing blades and a strainer basket) or other comminution aggregates such as cutting mills. The generated flake size is influenced by the hole diameter in the strainer basket. Metals are removed from the plastic waste while pre-sorting by means of magnetic and eddy current separators.
Conventionally, sorting according to colors and/or plastic types occurs before the comminution of the plastic waste. This is, however, associated with restrictions due to the contamination of the plastic waste because the identification rate of contaminated materials is less than with clean materials. Furthermore, several washing lines need to be operated when sorting before cleaning in order to clean the individual fractions. It is, however, also possible to first initially comminute plastic waste of different colors and/or different plastic types and then clean it, and only perform the sorting by colors and/or plastic types at the end of the process by means of color recognition, or respectively NIR, laser or x-ray spectroscopy. This can be done in an incident light process and/or a transillumination process with a suitable optical detector apparatus (e.g., a camera).
When recycling plastic flakes, in particular PET flakes, the following requirements must be satisfied:                1. Removal of film and cellulose labels;        2. Removal of cellulose;        3. Cleaning contaminants from contents from the flakes (such as beverage residue);        4. Cleaning adhering contaminants from the flakes (such as adhesives from labels);        5. Removal of metals (such as corrugated metal and aluminum cans);        6. Removal of foreign plastics; and        7. Sorting according to color (such as clear PET and colored PET).        
Similar requirements (however with higher thresholds) apply to the mechanical recycling of plastics. However, sorting according to color is generally omitted.
A method for removing cellulose and other adhering materials while recycling waste plastic, especially mixed plastic, is known from WO 2008/058750 A2. A toothed disk mill can be used with disks that have engaging teeth which are arranged spaced on concentric circles. Between the teeth of a circle, the gaps are large enough for pieces consisting of thicker or solid material to pass through freely. A disk mill is also known from DE 10 2005 013 693 A1.
However, sufficient cleaning of the impurities from the plastic waste is not always achieved in practice. This holds true in particular for the cleaning of flat shredded plastic. With such flat shredded plastic or flakes, folding can occur during cleaning so that only the outer surfaces are cleaned whereas the insides remain dirty.